Magnetic Particle Imaging (MPI) is a tomographic imaging technique, which relies on the nonlinearity of the magnetization curves of magnetic particles and the fact that the particle magnetization saturates at some magnetic field strength (Gleich et al., 2005, Nature, 435, 1214-1217). In a medical context MPI uses the magnetic properties of magnetic particles administered to the body to measure the particle concentration. Because a body contains no naturally occurring magnetic materials visible to MPI, there is no background signal. After intake, the MPI particles appear as bright signals in the images, from which particle concentrations can be calculated. By combining high spatial resolution with short image acquisition times, MPI can also capture dynamic concentration changes as the magnetic particles are moved. This allows MPI scanners to perform a wide range of functional measurements in a single scan.
Colon screening approaches are traditionally based on endoscopic colonoscopy, i.e. the examination of the colon and distal parts of the small bowel with a CCD camera or a fiber optic camera on a flexible tube passed through the anus. This technique allows for a visual diagnosis of the examined areas and grants the opportunity for biopsy and/or removal of lesions. However, endoscopic colonoscopy inter alia brings about a serious risk of gastrointestinal perforation which may be life threatening and requires immediate major surgery for repair.
An alternative, non-invasive technique is virtual colonoscopy or computed tomography (CT) colonography. CT colonography is a medical imaging method employing tomography created by computer processing. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around an axis of rotation. During the procedure the patient is typically placed in a supine position on the examination table. Subsequently a thin tube is inserted into the rectum, so that air can be pumped through the tube in order to inflate the colon for better viewing. The table then moves through the scanner to produce a series of two-dimensional cross-sections along the length of the colon while the patient is asked to hold his/her breath to avoid distortion on the images. Although CT colonography bears only a strongly reduced risk of gastrointestinal perforation (mainly due to gas distension), the method bears a severe risk of radiation exposure. The radiation dose from a CT colonography is considered to be equivalent to several hundred chest x-rays. Accordingly, the risk of developing solid tumors from radiation due to CT colonography is assumed to be substantially higher than the risk of perforation from colonoscopy.
Moreover, endoscopic colonoscopy as well as CT colonography require a bowel-cleansing regimen which typically includes a low-fiber or clear-liquid only diet for one to three days, followed by the administration of laxatives and large quantities of fluids the days before the screening. This procedure leads to a severe discomfort of the patients and drastically decreases their compliance.
Document WO 2009/074952 discloses an arrangement and a method for influencing and/or detecting magnetic particles in a region of action. An objection of the application is the provision of an enhanced apparatus and a more effective method for combined hyperthermia treatment and magnetic particle imaging (MPI).
Document WO 2008/078242 discloses a similar arrangement and method for influencing and/or detecting magnetic particles in a region of action. An objection of the application is the improvement of the quality of the magnetic field generating means and/or the quality of the magnetic field detecting means.
Weizenecker et al., 2009, Phys. Med. Biol., 54 (L1-L10) discloses a three-dimensional real-time in vivo magnetic particle imaging. The document indicates a temporal resolution of 21.5 ms achieved at a 3D field of view of 20.4×12×16.8 mm3 with a spatial resolution sufficient to resolve all heart chambers.
US 2006/0241391 discloses a method and system for the detection of pathologies, e.g. the detection of cancer in the gastrointestinal tract utilizing MRI technology.
A further alternative to endoscopic colonoscopy and CT colonography is Magnetic Resonance (MR) colonography, which is based on the Magnetic Resonance Imaging (MRI) technique, i.e. the use of magnetic fields to align the magnetization of atoms of magnetic particles in the body, and the corresponding employment of radio frequency fields to systematically alter the alignment of this magnetization, which causes the nuclei to produce a rotating magnetic field detectable by a scanner. However, in MRI approaches the thresholds for in vitro and in vivo imaging are such that the background signal from the host tissue is a crucial limiting factor, thus limiting the resolution power of the method. Furthermore, MR colonoscopy still requires bowel cleansing or at least a distention of the colonic lumen involving the administration of contrast agents such as barium via rectal tubes (Lauenstein et al., 2001, American Journal of Roentgenology, 177, 823-827), which still entails a high level of unpleasantness for the patient.
There is thus a need for an alternative colonography method, which has an elevated patient acceptance while allowing colon screenings at a high resolution.